diff --git a/centvrion/ast_nodes.py b/centvrion/ast_nodes.py
index 1c80e4a..3613566 100644
--- a/centvrion/ast_nodes.py
+++ b/centvrion/ast_nodes.py
@@ -47,6 +47,8 @@ def single_num_to_int(i, m):
 
 def num_to_int(n, m):
     chars = re.findall(r"[IVXLCDM]_*", n)
+    if ''.join(chars) != n:
+        raise Exception("Invalid numeral", n)
     nums = [single_num_to_int(i, m) for i in chars]
     new_nums = nums.copy()
     for x, num in enumerate(nums[:-3]):
diff --git a/tests/guessing.cent b/examples/guessing.cent
similarity index 100%
rename from tests/guessing.cent
rename to examples/guessing.cent